Well logging apparatuses are increasingly becoming more and more advanced, thus making it possible to obtain increasingly detailed information on well boreholes and the surrounding formations. As the logging apparatuses become more sophisticated, greater amounts of data are generated.
The logging apparatuses are suspended in well boreholes by logging cables, which provide electrical power and communications channels from the supporting surface equipment to the logging apparatuses. Logging cables have limited bandwidths; a typical short logging cable exhibits a signal bandwidth usable with prior art transmission methods of about 30 KHz. The usable bandwidth of the logging cable is determined by its length and the nature of the logging signal it must carry. The longer the cable the lower the usable bandwidth will be.
With its limited bandwidth, the logging cable forms a bottleneck, reducing the amount of data that can be transmitted uphole to the surface equipment. In systems that transmit analog waveforms over a logging cable, the transmission of faster analog waveforms result in unacceptable amplitude and phase distortion and obliteration of high frequency information. In systems that transmit digital data over a logging cable, the data transfer rate is limited.
Thus, the electrical characteristics of the logging cable limit the system logging speed, measurement resolution, or both.
Prior art methods involving direct amplitude and phase compensation of the logging cable are impractical. Many different types of logging cables are in use and each type has unique electrical characteristics. Compensation is further complicated by the dependance of the electrical characteristics of the logging cable on the length of cable in the borehole and the length of logging cable remaining on the drum. Furthermore, the amount and condition of the logging cable on each logging truck is unique.